DUBAI/UNITED NATIONS (Reuters) - Diplomats promoting a U.N. plan to end Yemen's war detect cautious support for its ideas from Saudi Arabia, raising hopes the proposals might unlock stalled efforts to end the 19-month-old conflict and a worsening humanitarian disaster.

The kingdom leads a mostly Gulf Arab military alliance which has launched thousands of air strikes in support of forces loyal to President Abd-Rabbu Mansour Hadi, who was driven into Saudi exile by the Iran-allied Houthi movement.

But the campaign failed to dislodge the group and their allies in Yemen's army from the capital Sanaa, and the U.N. proposal to end the stalemate envisions Hadi handing his powers to a less divisive deputy in exchange for the Houthis quitting main cities.

While both parties unofficially rejected the proposal last week, a senior diplomat at the United Nations told Reuters that Saudi Arabia appeared broadly to accept the initiative and had encouraged Hadi to deal with it.

"As far as I'm aware the Saudis have accepted the roadmap ... they have certainly done a very good job behind the scenes of encouraging Hadi to get closer on the spectrum of accepting it than he previously was," said the diplomat, who spoke on condition of anonymity.

The United Arab Emirates, another key country in the coalition, said last week that it supported the plan.

A prominent Saudi columnist wrote last week that the U.N. plan deserved further study.

"The legitimate government was too quick to denounce the peace initiative ... pushing for reconciliation requires both sides to pay a price," Abdulrahman al-Rashed wrote in the Arab News daily.

"We would definitely welcome support to President Hadi if he can impose a better solution whether by force or by agreement. But we know that this is not the case," Rashed added.

Saudi Arabia launched "Operation Decisive Storm" in Yemen in March 2015 in part to send a message to Iran that it would oppose by force the Islamic Republic's expanding political influence in the Arab world.

A Yemeni diplomatic source, also speaking on condition of anonymity, said that most, but not all, of the Saudi leadership had agreed to the plan.

The source added that concerns by the kingdom and Houthi officials about a withdrawal by the group from Yemen's population centers were being addressed by Oman, a neutral party in the regional power struggle.

"The Saudis are worried that the Houthis won't comply, while the Houthis fear it could expose them to attack. Oman told the Saudis it would use its influence with the Houthis to guarantee a withdrawal according to the U.N. plan," the source said.